Few details had previously emerged on Mursi's whereabouts since army chief General Abdel Fattah al-Sisi overthrew him and announced plans for elections.
Lawyer Mohamed Damati read on television what he said was a letter from the Islamist leader, who is still being detained, to the Egyptian people.
For the first time, Mursi indicated that he was held against his will as early as July 2, a day before the army announced his removal following mass protests against his rule.
"The kind Egyptian people should know that I have been kidnapped forcibly and against my will since July 2 and until July 5 in a Republican Guard house until I and my aide were moved again forcibly to a naval base belonging to the armed forces for four full months," Mursi was quoted as saying.
The Republican Guard is an elite military unit which protects the presidential palace and other government sites.
Mursi and other Islamists appeared in court on November 4 on charges of inciting violence in connection with the death of about a dozen protesters at the presidential palace in December. Most were members of Mursi's Muslim Brotherhood.
The letter marked the first time outside the courtroom that authorities allowed Mursi, who accuses the army of staging a coup, to tell his side of the story.
"Egypt will not recover until everything that happened due to this coup goes away...and the holding to account those who spilled blood everywhere on the nation's land," Mursi said.
"I salute the Egyptian people who rose up against this coup, which will fall by the power of the Egyptian people in their jihad for the sake of their rights and freedoms."
Security forces have mounted a crackdown against the Brotherhood, which won every election held since a popular uprisng toppled autocrat Hosni Mubarak in 2011.
Hundreds have been killed and thousands arrested, including the group's leaders. A court has banned the organisation.
Mursi said that while in detention, he had only met with European Union Foreign Policy Chief Catherine Ashton, an EU delegation and four prosecutors whose questions he refused to answer.
Damati said Mursi still refused to recognise the court which is trying him at a police academy .
If convicted, Mursi could face a life sentence or the death penalty.
